- a secondary structure occurring in many proteins, consisting of several polypeptide chains running in parallel or alternating directions and joined by intermolecular hydrogen bonds, creating a flexible, strong arrangement.
- A secondary structure that occurs in many proteins and consists of two or more parallel adjacent polypeptide chains arranged in such a way that hydrogen bonds can form between the chains. Unlike in an alpha helix where the amino acids form a coil, in beta sheets the amino acids are arranged in a zigzag pattern that forms a straight chain. The proteins in silk have a beta-sheet structure. Compare alpha helix random coil.